Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art exhaust a complex mixture of air pollutants. These air pollutants can include, among other things, gaseous compounds such as the oxides of nitrogen (NOX). Due to increased awareness of the environment, exhaust emission standards have become more stringent, and the amount of NOX emitted from an engine may be regulated depending on the type of engine, size of engine, and/or class of engine. In order to ensure compliance with the regulation of these compounds, some engine manufacturers have implemented a process called Selective Catalytic Reduction (SCR).
SCR is a process where a gaseous or liquid reductant (most commonly a urea/water solution) is added to the exhaust gas stream of an engine and is adsorbed onto a catalyst. The reductant reacts with NOX in the exhaust gas to form water (H2O) and elemental nitrogen (N2). Although SCR can be effective, the NOX-reduced emissions can only be realized as long as reductant of a proper quality is available in sufficient quantities for addition to the exhaust gas stream. That is, when a quality of the reductant is poor or when a supply of reductant is depleted, the reduction of NOX facilitated by SCR may be less than desired. For this reason, it can be important to monitor the quality and quantity of reductant available for use in the SCR process, and to diagnose and account for any associated deficiencies.
One system for monitoring an amount of available reductant is described in U.S. Patent Application Publication 2007/0137181 (the '181 publication), by Upadhyay et al. Specifically, the '181 publication describes an emissions control system for use with a diesel engine. The emissions control system has an SCR catalyst, a pair of NOX sensors, a temperature sensor, and a controller in communication with the NOX sensors and temperature sensor. The emissions control system reduces NOX through active injection of an aqueous urea solution into the exhaust gas entering the SCR catalyst. The NOX sensors provided upstream and downstream of the SCR catalyst, respectively, measure a concentration of NOX in the exhaust gas mixture.
During operation of the emissions control system described in the '181 publication, the controller first calculates a NOX reduction efficiency of the SCR catalyst. The controller then increases a temperature of the SCR catalyst by a predetermined amount to release a precise portion of reductant stored within the SCR catalyst. The controller then calculates the NOX reduction efficiency again, to determine an effect associated with the increased temperature. Based on the change in the NOX reduction efficiency of the SCR catalyst, the controller can determine how much reductant remains stored within the catalyst.
While the system of the '181 publication may be effective at estimating an amount of reductant stored within an SCR catalyst, it may not be effective at estimating a quality of that reductant or an amount of reductant available for injection upstream of the catalyst. Without accounting for a quality or quantity of reductant available for injection, proper operation of the emissions control system may not be possible. Further, the system of the '181 publication does not have any diagnostic capabilities to determine or account for quality or injection quantity related deficiencies.
The present disclosure is directed at overcoming one or more of the shortcomings set forth above and/or other problems of the prior art.